This invention relates to improvements in ozonator systems, and is primarily concerned with the ozone diffuser itself which functions to discharge ozone into a body of water or other liquid for an ozonation thereof.
Of the known basic ozonator systems, two are considered of specific interest with regard to the present invention. The first system involves the use of a static porous diffuser and must be operated at a positive pressure in order to force the ozone, and its carrier gas (air or oxygen), into the surrounding body of water through a porous ceramic or sintered stainless steel diffuser. Such porous diffusers are normally placed at the bottom of a tank of water and the gas filtered through the porous diffuser creating a column of small bubbles rising to the surface of the water being treated. The ozone and carrier gas in the small bubbles is partially dissolved into the water with the ozone gas that escapes, as the rising bubbles break at the surface, being removed and either destroyed or utilized at other points in the water treatment system. Such a system requires the use of energy consuming gas compressors and compressed air coolers at the input of the air preparation system. Further, the low gas-to-liquid transfer efficiency is a major factor which detracts from such static systems.
Another, more efficient, ozonator system basically follows techniques developed for use in the Swiss-made Kerag system, note for example the background material in applicant's prior U.S. Pat. No. 4,156,653. Such a system utilizes a motorized diffuser which provides a negative pressure or suction to draw the carrier gas through the entire air preparation and ozone generating cells of the ozonator with the ozone ultimately mixing and discharging with a thin sheet of high velocity water generated by a rather complex rotating turbine.
The effectiveness of such a system in ozonating the surrounding body of water is extremely high. However, the motorized diffuser is a complex and expensive device which requires a positioning of the operating components, including the turbine itself and at least the lower portion of the drive shaft, in a submerged environment within the body of liquid being ozonated.
It is operationally desirable to place the rotating turbine near the bottom of the water tank in which the diffuser is located. However, because of potential problems with shaft end whip, and the like, the length of the drive shaft for the turbine has to be limited, this in turn determining the optimum vertical location of the turbine within the tank.
When five to ten minute ozone retention times in the water being processed with ozone is required, the height limitation of the tank in which the diffuser is placed requires a following tank to achieve the longer retention times. Such additional tanks must be made of an appropriate, and normally quite expensive, ozone resistant material.
Other problems and expenses arise from the precision machining and careful balancing required for the assembly, the considerable thickness and stiffness required for the drive shaft, and a normally elaborate system of seals, bearings, moisture sensors, and the like.
In operation, the diffuser with the turbine-like rotor at the lower end of the shaft sucks water from below the turbine through a water intake screen into the center portion of the turbine. The vanes of the rotating turbine impart pressure to this input water which in turn is ejected outward at high velocity as a thin horizontal sheet about a full 360.degree. circle. The sheet of high velocity water subsequently passes outward through a slot in the surrounding shroud. The shape of the shroud about the slot forms a modified circular venturi with the action of the water passing through the venturi section of the shroud creating a negative pressure for a sucking of the carrier gas and ozone through the shroud for ejection with the high velocity water. The water intake screen is considered necessary to prevent entry of water-borne particles into the rotating turbine which could cause pitting of the blades or clogging of the passages, and ultimately an elaborate removal, disassembly and cleaning of the components.
Another less than desirable feature in the driven turbine diffuser is that the drive motors are designed to run at a constant speed. Due to this constant turbine speed, the range of gas flow for proper operation is limited as compared to the range of gas flow allowed through the ozonator.
For example, gas flow through the ozonator can be 5:1. However, permitted gas flow variance into the constant speed diffuser is in the order of 3:1.
Increase of the permissible diffuser gas flow minimum and maximum to match the ozonator gas flow can be done using a variable motor speed controller or by restricting the water inlet to the turbine using a fixed orifice plate. However, the fixed orifice plate must be mechanically removed or installed, a costly time-consuming process to modify gas flow. Further, variable motor speed devices are in themselves quite expensive.